The research published in the Journal of Reproduction found male mice babies had a smaller number of neurons in brain areas connected to sexual behaviour when their mothers were fed paracetamol while pregnant.

These male mice pups were also found to be less aggressive than those born to mothers who were not exposed to paracetamol.

It could lead to female infertility among adult rodents and malformations in newborn boys.

Dr Rachel Hall the head of the Behavioural Neuroscience laboratory at Monash Medical Center says the perceived safety of paracetamol use in pregnancy is based on findings about absence of birth defects and maternal and neonatal wellbeing.

The medication’s long term effects on reproductive behaviour have never been assessed before, she says.

“The prenatal brain is particularly vulnerable as during this period several critical regions of the brain are forming and connecting to other regions,” she says.

“Therefore, factors that would generally not impact an adult brain could have severe effects on the developing prenatal brain.”

Dr Hall says the zika virus is a good example of how an external factor has no effect on the adult brain but devastating effects on the foetal brain.

“The research would suggest that Australian pregnant women should take caution when taking regular pain relief medication and consider the long-term impact these medications may be having on their developing child,” she said.

A lower dose of paracetamol in the mice did not have any effect on brain structure or behaviour in the study, he said.

“It is to be hoped that pregnant women who have taken the occasional tablet of paracetamol because they have a headache or fever will not be alarmed by this study,” he said.

UK expert from Cambridge Prof Ieuan Hughes, Emeritus Professor of Paediatrics University of Cambridge, said he’s not convinced the amount of paracetamol used in mice is comparable to the way the drug is used by pregnant women.

“In the animal study exposure to paracetamol was daily from 7 days post-coitum to birth. Pregnant women generally take analgesics like paracetamol intermittently for symptoms and generally for a very short period,” he said.

“It is my view that there is not sufficient evidence in humans to deter pregnant women taking the occasional paracetamol for symptomatic reasons,” he said.